A simplest example of MRAM that is a typical resistance change type memory has a structure called 1T/1R. The greatest problem in this memory structure is how a large amount of current is flowed from a transistor to a resistance change element in a determined cell area.
If a cell transistor size is miniaturized in accordance with a finer area of the cell, various difficulties should occur. One of the difficulties is that a device performance is deteriorated (i.e., an off-leakage current is increased) due to a short channel effect based on a shorter gate length. Another difficulty is that if a cell area is to be reduced, contact regions for source and drain electrodes also become smaller. Therefore, the increase in a parasitic resistance (contact resistance) at this part gives a serious influence to deterioration of a current drive.
In future, suppression of the short channel effect and enhancement of performance of the current drive need to be attempted by forming so called a multi-gate device. In this case, a device layout in which a transistor can be easily arranged should be required.